(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD), and in particular, to a four color filter (RGBW) LCD.
(b) Description of the Related Art
An LCD is one of the most popular flat panel displays. Generally, a liquid crystal display has two substrates with electrodes, and a liquid crystal layer sandwiched between the two substrates. Voltages are applied to the electrodes so that the liquid crystal molecules in the liquid crystal layer are re-oriented to thereby control light transmission.
A basic LCD has two substrates respectively having electrodes for producing an electric field. One of the two substrates has a plurality of pixel electrodes arranged in a matrix shape, and the other has a common electrode covering the entire display area of the substrate.
The liquid crystal display has a plurality of pixels with pixel electrodes and color filters of red, green, and blue. The pixels are driven by way of signals applied through the wiring lines. The wiring lines include scanning signal lines or gate lines for carrying scanning signals, and picture signal lines or data lines for carrying the picture signals. Thin film transistors are formed at the respective pixels while each is connected to one gate line and one data line. The picture signals applied to the pixel electrodes are controlled by way of the thin film transistors.
There are several types of arrangement with the color filters of red, green, and blue. Among them are a stripe type where the color filters of the same color are arranged at the respective pixel columns; a mosaic type where the color filters of red, green, and blue are sequentially arranged in the pixel row and column directions; and a delta type where the pixels are zigzag-alternated in the pixel column direction, and the color filters of red, green, and blue are sequentially arranged at the pixels. In the case of the delta type, the three unit pixels with the color filters of red, green, and blue are operated as one dot, and this makes it easy to express a circle or a diagonal line.
The Clairvoyante, Inc. laboratories have proposed a pixel arrangement structure called the “PenTile Matrix™,” which has a high resolution expression capacity advantageous in displaying pictures while involving minimized design cost. In such a pixel arrangement structure, the unit pixel of blue is common to two dots, and the neighboring blue pixels receive the data signals from one data driving IC while being driven by two different gate driving ICs. With the use of the PenTile Matrix pixel structure, the resolution of the UXGA level can be realized by way of a display device of the SVGA level. Furthermore, the number of low-cost gate driving ICs is increased, but the number of high-cost data driving ICs is decreased. This minimizes the design cost for the display device.
However, the PenTile Matrix pixel structure has defects such as the arrangement of gate lines and data lines is complex and the aperture ratio is low because the complex gate lines and data lines diminish the aperture area. Further, a difference of pixel area among the red, green, and blue pixels induces a difference of pixel parameters such as storage capacitance (Cst) and liquid crystal capacitance (Clc). This difference of pixel parameters results in display defects such as flicker.
A four color LCD (RGBW LCD) using red (R), green (G), blue (B), and white (W) color filters is being developed for increasing brightness. There are two types of RGBW LCD, which are distinguished by their arrangement of color filters. One is a stripe type and the other is a checkerboard type. In a stripe type of LCD, a dot comprise four pixels of red, green, blue, and white, and the number of data lines is increased by 25% over an LCD using only red, green, and blue color filters. In a checkerboard type, the number of data lines is decreased by 30% with respect to an LCD using only red, green, and blue color filters, but the number of gate lines is increased by twice compared to an LCD using only red, green, and blue color filters. For solving such a problem, a white pixel may share the area of one of the red, green, and blue pixels. In particular, it is appropriate for a blue pixel to share its area with the white pixel.